Deflection compensation for temperature changes in a color picture tube

ABSTRACT

In a color picture tube having an apertured beam selecting grill or mask through one or more electron beams are made to land on predetermined color phosphors applied to the face plate of the tube, thermal expansion of the grill or mask is compensated for, so as to avoid mislanding of the beam or beams, by providing an auxiliary magnetic deflection means located in back of the main magnetic deflection or scanning means and operative in dependence on the operation of the main deflection means to produce magnetic flux in opposition thereto. The current flowing in the auxiliary magnetic deflection means is decreased with increasing temperature by means of a thermosensitive magnetic means so as to similarly decrease the magnetic flux opposing that of the main deflection means, whereby the effective center of deflection of the beam or beams is shifted rearwardly in response to increasing temperature.

Bite States atent Tokita et al.

[54] DEFLECTION COMPENSATION FOR TEMPERATURE CHANGES IN A COLOR PICTURETUBE [72] Inventors: Tetsuo Tokita; Yuzo Fuse; Yoshiharu Katagiri, allof Tokyo, Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22]Filed: Feb. 11, 1970 [21] Appl. No.: 10,369

[451 June 6,1972

3,524,093 8/1970 Burdick et al. "313/75 Primary Examiner-Rodney D.Bennett, Jr.

Assistant Examiner-H. A. Birmiel AnorneyLewis H. Eslinger, AlvinSinderbrand and Curtis, Morris & Safford [57] ABSTRACT In a colorpicture tube having an apertured beam selecting grill or mask throughone or more electron beams are made to land on predetermined colorphosphors applied to the face plate of the tube, thermal expansion ofthe grill or mask is compensated for, so as to avoid mislanding of thebeam or beams, by providing an auxiliary magnetic deflection meanslocated in back of the main magnetic deflection or scanning means andoperative in dependence on the operation of the main deflection means toproduce magnetic flux in opposition thereto. The current flowing in theauxiliary magnetic deflection means is decreased with increasingtemperature by means of a thermosensitive magnetic means so as tosimilarly decrease the magnetic flux opposing that of the maindeflection means, whereby the effective center of deflection of the beamor beams is shifted rearwardly in response to increasing temperature 8Claims, 8 Drawing Figures DEFLECTION COMPENSATION FOR TEMPERATURECHANGES IN A COLOR PICTURE TUBE This invention relates generally tocolor picture tubes, and more particularly is directed to compensatingfor the mislanding of the electron beam or beams that may result fromtemperature variations in the tube.

A color picture tube generally includes an electron beam selectingdevice, such as, an apertured mask, grill or grid, disposed within thetube adjacent the screen of color phosphors applied to the face plate ofthe tube, and by which each beam is made to land on a predeterminedcolor phosphor in dependence on the angle of incidence of the beam withrespect to the beam selecting device when passing through an aperture ofthe latter. During operation of the color picture tube, the impingementof the electron beam or beams on the beam selecting device increase thetemperature of the latter and thereby effects thermal expansion of thelatter. Such thermal expansion changes the positions or alignments ofthe apertures of the beam selecting device in relation to the respectivesets or arrays of color phosphors of the screen, and the change inalignment increases progressively from the center of the beam selectingdevice toward the periphery of the latter. The change in positions oralignment of the apertures relative to the respective sets or arrays ofcolor phosphors results in mislanding of the beams, that is, in theimpingement of the beams on other than the respective color phosphors ofthe screen, and this causes deterioration of the color purity of theresultant picture on the screen.

In order to avoid the described mislanding of the beams resulting fromthennal expansion of the beam selecting device, it has been proposed toreduce the distance from the beam selecting device to the screen as thetemperature of the beam selecting device increases. However, mountingthe beam selecting device for temperature responsive movement relativeto the screen requires the use of complicated structures for supportingthe beam selecting device and such structures have reduced resistance toshocks or impacts.

Another previously proposed arrangement for avoiding the describedmislanding of the beams resulting from variations in the temperaturewithin the tube, includes an auxiliary deflection coil mounted on theneck of the tube, for example, adjacent the main deflection yoke bywhich the beam or beams are horizontally and vertically deflected so asto scan the screen, and a circuit by which a deflection current is madeto flow through the auxiliary deflection coil and is varied in responseto changes in the temperature of the beam selecting device. Suchvariation of the deflection current is selected so that the magneticfield produced by the auxiliary deflection coil serves to shift theeffective center of beam deflection in response to temperature changesand thereby maintains proper landing of the beams on the respectivecolor phosphors. However, such proposed arrangement does not providesufficient compensation for fully and reliably avoiding the describedmislanding, and the circuit required for varying deflection current inresponse to changes of temperature is complex and costly.

Accordingly, it is an object of this invention to provide a relativelysimple and reliable arrangement by which the effective center of beamdeflection in a color picture tube is shified in response to temperaturevariations in the tube so as to effectively compensate for themislanding of the beam or beams that would otherwise result from thethermal expansion or distortion of the beam selecting device.

Another object is to provide a compensating arrangement, as aforesaid,which is operable by a current supplied to the main deflection yoke ofthe tube for effecting the horizontal and/or vertical deflections of thebeam or beams, and in which such current for operating the compensatingarrangement is controlled by a simple, inexpensive and reliable circuitincluding a thermo-sensitive magnetic means.

In accordance with an aspect of this invention, a color picture tube isprovided with an auxiliary magnetic deflection means disposed in back ofthe main deflection yoke and being operative by a current passingthrough a coil of the main deflection yoke to produce magnetic flux inopposition to the magnetic flux provided by the latter, with suchcurrent for operating the auxiliary magnetic deflection means beingsupplied to the latter by way of a circuit including a thermo-sensitivemagnetic means that decreases the current to the auxiliary magneticdeflection means with increasing temperature so as to similarly decreasethe magnetic flux acting in opposition to the magnetic flux produced bythe main deflection yoke, whereby the effective center of deflection ofthe beam or beams by the combined effects of the main deflection yokeand the auxiliary deflection means is shifted rearwardly in accordancewith increasing temperature to compensate for thermal expansion of thebeam selecting device.

More particularly, in a compensating arrangement according to anembodiment of this invention, the auxiliary magnetic deflection meansincludes a coil or coils wound on a magnetic core and connected with thecorresponding coil or coils of the main deflection yoke by way of acircuit having the coil or coils of the auxiliary deflection means inparallel with a winding on a magnetic core of a permeability whichdecreases with increasing temperature of the tube so that the inductanceof such winding decreases with increasing tube temperature. In otherembodiments of this invention, the coil or coils of the auxiliarydeflection means may receive the current for operation of the latterfrom the secondary winding of a transformer having a magnetic core of apermeability that decreases with increasing tube temperature and aprimary winding connected with the corresponding coil or coils of themain deflection yoke.

The above, and other objects, features and advantages of this invention,will be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawings wherein:

FIG. IA is a schematic, axial sectional view of a color picture tube towhich reference will be made in explaining the mislanding of an electronbeam that may result from thermal changes within the tube;

FIG. 1B is an enlarged detail view of a portion of the structure shownon FIG. IA, and to which particular reference will be made in explainingthe compensation efi'ected according to this invention;

FIG. 2 is a schematic elevational view, as viewed from the top, of acolor picture tube provided with a temperature compensating deviceaccording to this invention;

FIG. 3 is a schematic front elevational view of an auxiliary deflectionyoke included in the device of FIG. and a wiring diagram of a circuitfor 2 and the operating current thereto according to one embodiment ofthis invention;

FIG. 4 is a graph illustrating the variation of inductance with changingtemperature for an element included in the circuit of FIG. 3;

FIG. 5 is a graph illustrating the current flow through the coils of theauxiliary deflection yoke for different tube temperature; and

FIGS. 6 and 7 are wiring diagrams of circuits for supplying theoperating current to the coils of the auxiliary deflection yokeaccording to two other embodiments of the invention.

Referring to the drawings in detail and initially to FIG. 1A thereof, itwill be seen that a color picture tube 1, as there illustrated, has aphosphor screen 2 formed on the inner surface of its face plate and anapertured beam selecting device 3, for example, in the form of a shadowmask or aperture grill or grid suitably supported within the tube andspaced rearwardly from the phosphor screen 2. As is well known andparticularly shown on FIG. 1B, the phosphor screen 2 is made up of setsor arrays of primary color phosphors, as indicated at R, G and B, andthe purpose of the beam selecting device 3 is to determine which of thecolor phosphors a particular electron beam lands upon in dependence onthe angle of incidence of the beam with respect to device 3 at anaperture 4 of the latter through which the beam passes prior toimpinging against the corresponding set or array of color phosphors. Itwill be understood that the beam selecting device 3 is heated by theimpingement of the electron beam or beams thereon during scanning of thescreen, and such heating of the beam selecting device causes its thermalexpansion, for example, from the condition shown in full lines on FIGS.1A and 1B to the condition shown in broken lines at 3', where the beamselecting device is spaced rearwardly from its normal or actual positionmerely for convenience of illustration. It will be seen that the thermalexpansion of the device 3 to the condition indicated at 3' results inthe displacement of the apertures 4 away from the central axis xx of thetube, and that the extent of such displacement of the aperturesincreases progressively towards the periphery of the screen 2 and thebeam selecting device. Thus, for example, with respect to the aperture4a, the heating of the beam selecting device 3 will effect thedisplacement of such aperture away from the tube axis to the positionindicated at 4'a.

Assuming that an electron beam B is deflected about the effective center0, as by the usual main deflection yoke 6 provided on the color picturetube 1, so as to follow the path 5 through the aperture 4a of beamselecting device 3 and to land on the corresponding color phosphor G, ofthe array or set A when the beam selecting device 3 is at a relativelylow temperature, it will be apparent that, in response to heating andthe resulting thermal expansion of the beam selecting device, theelectron beam B; will be in a position 5' when it passes through thedisplaced aperture 4'0 and thus will no longer land on the correspondingcolor phosphor G but rather will misland on the color phosphor R, withresulting deterioration of the color purity of the picture.

However, if the effective center of deflection of the beam B is shiftedfrom the position in FIG. 1A in the rearward direction, that is, awayfrom the screen 2 or beam selecting device 3, for example, to theposition 0', the beam, when deflected to the position will pass throughaperture 4a of the thermally expanded beam selecting device 3' and againland on the corresponding color phosphor G of the respective phosphorset A, whereby to compensate for the thermal expansion of the beamselecting device and to avoid deterioration of the color purity of thepicture. Thus, mislanding of the electron beam or beams can be avoidedby suitably shifting the efiective center of deflection of each electronbeam in response to temperature changes within the tube.

In accordance with the present invention, particularly as illustrated onFIG. 2, a color picture tube 1 having an electron gun 7 directing threebeams B B and B toward color screen 2 and causing such beams to convergeat a common aperture of the beam selecting device 3 is provided with anauxiliary magnetic deflection device or yoke 8 in addition to the usualmain deflection yoke 6 by which the three beams are deflectedhorizontally and vertically so as to scan the screen. When the colorphosphors of screen 2 are applied in the form of vertical stripes andbeam selecting device 3 is constituted by an aperture grill havingvertical slits therein corresponding to the respective sets or arrays ofcolor phosphor stripes, then the auxiliary deflection device 8 accordingto this invention need provide mislanding compensation only with respectto the horizontal deflections of the beams.

As shown on FIG. 2, the auxiliary deflection device 8 is mounted on theneck of tube 1 at the side of main deflection yoke 6 remote from screen2, that is, in back of yoke 6, and comprises an annular magnetic core 10and two coil portions 1 la and 11b (FIG. 3) which are electricallyconnected, for example, in parallel, and wound on opposed side portionsof core 10 so that, in response to a current flow through coil portions11a and 11b, there is produced a magnetic flux, as indicated at F or Fon FIG. 3, to effect horizontal deflections of the beams B B and B Asindicated on FIG. 3, the coil portions Ila and 11b of device 8 areconnected, for example, in series, with the horizontal deflection coilsor windings 6H of the main deflection yoke 6 so that, when a horizontaldeflection current is supplied to coils 6H by way of terminals 90 and 9bto effect horizontal scanning deflection of the beams, a

current will also flow in coil portions lla and 11b to produce themagnetic flux F or F in opposition to the magnetic flux produced by thecurrent flowing in the coils 6H.

In accordance with this invention, the current supplied to coil portions11a and 11b to produce the magnetic flux F or F is controlled by acircuit that includes a thermo-sensitive element 12 having a magneticcore, the permeability of which decreases with increasing temperature,and a winding or windings on such core connected with the coil portionslla and 11b so as to decrease the current flowing through the latter asthe penneability of the core decreases with increasing temperature. Thethermo-sensitive element 12 is suitably mounted at a location adjacentthe tube, for example, against the outer surface of the funnel portionof the tube envelope 1, as shown, or against the outer surface of theneck portion of the tube envelope, where the temperature variessimilarly to the temperature variations of the beam selecting device 3.

In the embodiment of the invention shown in FIG. 3, the thennosensitiveelement 12 is in the form of a variable inductance element including awinding 13 connected in parallel with coil portions 1 la and 11b andbeing wound on a core 14 having a permeability that decreases withincreasing temperature, for example, having the permeabilitycharacteristic illustrated on FIG. 4. As mentioned above, the coilportions and llb are wound so that, when the deflection current flowsthrough deflection coils 6H to produce the flux H or H of the maindeflection field, the portion of that current passing through the coilportions 1 1a and 11b produces an auxiliary or pre-deflection fieldhaving its flux F or F, respectively, in 0pposition to the flux H or H.Further, it will be apparent that the current flowing through coils 6His divided between coil portions 11a and 11b and the winding 13 ofelement 12 in dependence on the inductance of the latter.

When the operation of tube '1 is initiated, that is, when core 14 isrelatively cool and has a high permeability, the inductance of element12 is correspondingly high so that the major portion of the horizontaldeflection current flowing through coils 6H passes also through coilportions 11a and 1 1b, for example, as indicated by the full line 15 onFIG. 5. As a result of such current flowing through coil portions Ilaand 11b, the auxiliary deflection yoke or device 8 produces a strongflux which causes a relatively large pre-deflection of the beam inadvance of the deflection caused by main deflection yoke 6, whereby thebeam follows the path indicated at 5 on FIG. 1. Such path 5 has thedeflection center 0 which is appropriate for the condition of the beamselecting device 3 prior to the thermal expansion of the latter. As thebeam selecting device 3 is expanded due to the heating thereofcoincident to continued operation of tube 1, the core 14 of element 12is similarly heated so as to decrease the permeability of core 14 andcorrespondingly decrease the inductance of element 12. By reason of suchdecreased inductance, the horizontal deflection current flowing throughcoils 6H is increasingly divided between coil portions lla and 11b andwinding 13, that is, the proportion of the horizontal deflection currentflowing through coil portions 11a and 1 lb is reduced, for example, asindicated by the broken line 15' on FIG. 5. The reduction of the currentflowing in coil portions 110 and 1 lb similarly reduces the resultingflux F or F which causes a small pre-deflection of the beam in advanceof the main deflection by yoke 6, whereby the beam follows the pathindicated at 5 on FIG. 1. Such path 5" has its deflection center at thelocation 0, that is, shifted rearwardly with respect to the originaldeflection center 0, to ensure the proper landing of the beam on therespective phosphor for the thermally expanded condition of the beamselecting device 3.

Referring now to FIG. 6, it will be seen that, in another embodiment ofthe invention, the thermo-sensitive element 12A, through which the coilportions 11a and llb of auxiliary deflection yoke 8 are connected withthe coils 6H of the main deflection yoke, is in the form of athermo-sensitive transformer including primary and secondary windings 16and 17 which are separately wound on a core 18 having a permeabilitywhich decreases with increasing temperature. The thermosensitivetransformer 12A has its primary winding 16 connected in series withcoils 6H of the main deflection yoke so that the horizontal deflectioncurrent flows therethrough, and the coil portions 110 and 11b of theauxiliary deflection yoke are connected with secondary winding 17.

It will be apparent that, in the embodiment of FIG. 6, when the tube andhence the core 18 are relatively cool, the high permeability of the corecauses a relatively large current to be induced in secondary winding 17and to flow through the coil portions 11a and 11b in response to thehorizontal deflection current flowing through primary winding 16. On theother hand, with increasing temperature of the tube and hence of thecore 18, the decreased permeability of the core reduces the currentinduced in winding 17 and flowing through coil portions 110 and 11b.Thus, as described previously with reference to FIGS. 1 and 3,increasing temperature of the tube is accompanied by decreasingpredeflection of the beam by auxiliary deflection yoke 8 so that thedeflection center of the beam is shifted rearwardly to compensate forthe thermal expansion of the beam selecting device 3.

The auxiliary deflection yoke 8 provided according to this invention maybe further utilized to compensate for deviations of the beam or beamsfrom a desired path, for example, deviations resulting from relativemisalignment of the tube parts occurring in the course of the assemblyof the tube. For example, as shown on FIG. 7 in which the circuit isgenerally similar to that described with reference to FIG. 6, a DCcurrent or bias may be applied to coil portions 11a and 1 lb ofauxiliary deflection yoke 8 from an adjustable DC source 19. Aninductance may be connected between DC source 19 and coil portions 11aand 11b so that the pre-deflection current flowing through the latterwill not also flow through source 19. Further, as shown, a capacitor 21is preferably interposed between DC source 19 and secondary winding 17of transformer 12A so that the DC current will not flow through thetransformer, and thus cannot influence the compensation provided tocorrect for mislanding of the beam or beams.

In the foregoing description of embodiments of the invention, it hasbeen assumed that the color phosphors of screen 2 are applied in theform of vertical stripes and beam selecting device 3 is constituted byan aperture grill with vertical slits so that mislanding compensation isrequired only with respect to horizontal deflection of the beam orbeams. However, when the color picture tube has a shadow mask as itsbeam selecting device and the color phosphors are applied in sets orarrays of dots, then it is necessary to compensate for temperatureinduced mislanding in the vertical, as well as the horizontaldirections. Such mislanding compensation in the vertical direction canbe effected by providing additional coil portions (not shown) on the topand bottom portions of core 10, and by connecting the additional coilportions with the vertical deflection coils of main yoke 6 throughcircuits similar to those described with reference to FIGS. 3, 6 and 7.

Although illustrative embodiments of the invention have been describedin detail herein with reference to the drawings, it is to be understoodthat the invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein withoutdeparting from the scope or spirit of the invention.

What is claimed is:

1. In a color picture tube including an envelope having a face plate, ascreen of phosphors coated on said face plate, an electron gun devicefor generating at least one electron beam directed toward said faceplate, apertured beam selecting means disposed adjacent said face plateto land said beam on selected phosphors of said screen in accordancewith the angle of incidence of said beam to said beam selecting means atthe apertures of the latter, and main magnetic deflection means fordeflecting said beam so as to cause scanning of said screen; theimprovement comprising auxiliary magnetic deflection means disposed atthe side of said main deflection means remote from said screen, andcircuit means connecting said auxiliary magnetic deflection means withsaid main magnetic deflection means to cause a current flow through saidauxiliary deflection means for producing a magnetic flux in oppositionto that produced by the main deflection means in response to thesupplying of a deflection current to said main deflection means, saidcircuit means including an element sensitive to the temperature of saidtube and having a magnetic core member with a permeability thatdecreases with increasing temperature and at least one winding wound onsaid core member and connected with said auxiliary deflection means todecrease said current flow through the latter with increasingtemperature of said tube, whereby said magnetic flux produced by theauxiliary deflection means is similarly decreased and the angle ofincidence of the beam to the beam selecting means is changed tocompensate for thermal expansion of said beam selecting means.

2. A color picture tube according to claim 1, in which said maindeflection means includes coil means to produce the magnetic flux fordeflecting said beam upon the flow of said deflection currenttherethrough, and said auxiliary deflection means includes a core andadditional coil means wound on said core and electrically connected withsaid coil means of the main deflection means by said circuit means toproduce said magnetic flux in opposition to the flux of said maindeflection means in response to said current flow.

3. A color picture tube according to claim 2, in which said auxiliarydeflection means is disposed adjacent to said main deflection means.

4. A color picture tube according to claim 2, in which said coil meansof the main deflection means includes horizontal and vertical deflectioncoils to produce magnetic flux for deflecting said beam horizontally andvertically, respectively, said additional coil means is connectedelectrically by way of said circuit means with said horizontaldeflection coil and is arranged to deflect said beam horizontally inopposition to the horizontal deflection of said beam resulting from saiddeflection current flow through said horizontal coil said phosphors arein the form of vertical stripes on said face plate, and said aperturesof the beam selecting means are in the form of vertical slits.

5. A color picture tube according to claim 1, in which said elementsensitive to the temperature of the tube is a variable inductance meanshaving said one winding thereof connected in parallel with saidauxiliary deflection means to said main deflection means so that saiddeflection current is proportioned between said auxiliary deflectionmeans and said inductance means in dependence on the temperature sensedby said core member of variable permeability.

6. A color picture tube according to claim 1, in which said elementsensitive to the temperature of the tube is in the form of a transformerhaving a primary winding in addition to said one winding, and saidprimary winding is connected with said main deflection means to receivesaid deflection current and to induce said current flow in said onewinding by way of said core member of variable permeability.

7. A color picture tube according to claim I, in which an adjustable DCcurrent source is also connected with said auxiliary deflection means tocause the latter to compensate for deviations of said beam from adesired path.

8. A color picture tube according to claim 7, in which said elementsensitive to the temperature of the tube is in the form of a transformerhaving a primary winding in addition to said one winding, said primarywinding is connected with said main deflection means to receive saiddeflection current and to induce said current flow in said one windingby way of said core member of variable permeability, and means areprovided to isolate said transformer from the influence of DC currentfrom said source and to isolate said source from said current flowinduced in said one Winding.

1. In a color picture tube including an envelope having a face plate, ascreen of phosphors coated on said face plate, an electron gun devicefor generating at least one electron beam directed toward said faceplate, apertured beam selecting means disposed adjacent said face plateto land said beam on selected phosphors of said screen in accordancewith the angle of incidence of said beam to said beam selecting means atthe apertures of the latter, and main magnetic deflection means fordeflecting said beam so as to cause scanning of said screen; theimprovement comprising auxiliary magnetic deflection means disposed atthe side of said main deflection means remote from said screen, andcircuit means connecting said auxiliary magnetic deflection means withsaid main magnetic deflection means to cause a current flow through saidauxiliary deflection means for producing a magnetic flux in oppositionto that produced by the main deflection means in response to thesupplying of a deflection current to said main deflection means, saidcircuit means including an element sensitive to the temperature of saidtube and having a magnetic core member with a permeability thatdecreases with increasing temperature and at least one winding wounD onsaid core member and connected with said auxiliary deflection means todecrease said current flow through the latter with increasingtemperature of said tube, whereby said magnetic flux produced by theauxiliary deflection means is similarly decreased and the angle ofincidence of the beam to the beam selecting means is changed tocompensate for thermal expansion of said beam selecting means.
 2. Acolor picture tube according to claim 1, in which said main deflectionmeans includes coil means to produce the magnetic flux for deflectingsaid beam upon the flow of said deflection current therethrough, andsaid auxiliary deflection means includes a core and additional coilmeans wound on said core and electrically connected with said coil meansof the main deflection means by said circuit means to produce saidmagnetic flux in opposition to the flux of said main deflection means inresponse to said current flow.
 3. A color picture tube according toclaim 2, in which said auxiliary deflection means is disposed adjacentto said main deflection means.
 4. A color picture tube according toclaim 2, in which said coil means of the main deflection means includeshorizontal and vertical deflection coils to produce magnetic flux fordeflecting said beam horizontally and vertically, respectively, saidadditional coil means is connected electrically by way of said circuitmeans with said horizontal deflection coil and is arranged to deflectsaid beam horizontally in opposition to the horizontal deflection ofsaid beam resulting from said deflection current flow through saidhorizontal coil said phosphors are in the form of vertical stripes onsaid face plate, and said apertures of the beam selecting means are inthe form of vertical slits.
 5. A color picture tube according to claim1, in which said element sensitive to the temperature of the tube is avariable inductance means having said one winding thereof connected inparallel with said auxiliary deflection means to said main deflectionmeans so that said deflection current is proportioned between saidauxiliary deflection means and said inductance means in dependence onthe temperature sensed by said core member of variable permeability. 6.A color picture tube according to claim 1, in which said elementsensitive to the temperature of the tube is in the form of a transformerhaving a primary winding in addition to said one winding, and saidprimary winding is connected with said main deflection means to receivesaid deflection current and to induce said current flow in said onewinding by way of said core member of variable permeability.
 7. A colorpicture tube according to claim 1, in which an adjustable DC currentsource is also connected with said auxiliary deflection means to causethe latter to compensate for deviations of said beam from a desiredpath.
 8. A color picture tube according to claim 7, in which saidelement sensitive to the temperature of the tube is in the form of atransformer having a primary winding in addition to said one winding,said primary winding is connected with said main deflection means toreceive said deflection current and to induce said current flow in saidone winding by way of said core member of variable permeability, andmeans are provided to isolate said transformer from the influence of DCcurrent from said source and to isolate said source from said currentflow induced in said one winding.